-.B LABEL
-device label or serial number, like USB serial number, SCSI UUID or
-file system label. Up to 5 different sysfs files can be checked, with
-all of the values being required in order to match the rule. The
-.B BUS
-key is optional, but if specified, the sysfs device bus must be able to be
-detemined by a "device" symlink.
-.br
-.RB "keys: " BUS ", " SYSFS_